1. Field of the Invention
The present invention relates to a magnetic recording medium having a magnetic recording layer formed in a predetermined convex-concave pattern on a substrate and thus having so-called servo areas and information data areas (a magnetic recording medium of a discrete type) and further relates to a magnetic recording and reproducing apparatus including such a magnetic recording medium and a magnetic head for detecting servo signals on the medium and recording and reproducing information data on and from the medium.
2. Description of the Related Art
Improvement in areal recording density of magnetic recording mediums such as hard disks has conventionally been achieved by techniques of both (1) improving the linear recording density and (2) improving the track density. In order to achieve further and higher densification in future, it is necessary to improve the areal recording density based on the foregoing both techniques.
With respect to improving the track density, there have been raised problems of processing limitation about magnetic heads, side-fringe or crosstalk caused by expansion of magnetic fields of magnetic heads, and so forth, and therefore, it can be said that the improvement in areal recording density by progressing the track-density increasing technique for magnetic heads, which is merely an extension of the conventional improvement technique, has reached the limit.
On the other hand, as a technique of improving the linear recording density, reduction in layer thickness and higher coercive forces have been achieved in conventional longitudinal magnetic mediums. However, in terms of further and higher densification of the mediums and stability of recording magnetization against thermal fluctuation, attention has been paid to perpendicular magnetic recording mediums.
Under these circumstances, as a technique of improving the areal recording density and supplementing the higher track densification of the magnetic heads, there have been proposed magnetic recording mediums of a discrete track disk type in which a recording layer is formed in a predetermined convex-concave pattern. For example, JP-A-H11-328662 discloses a magnetic recording medium in which predetermined convex and concave portions are formed on a substrate and a perpendicular magnetic layer in the form of a single layer is formed along the convex and concave portions.
A reduction in spacing is necessary for accomplishing an increase in recording density. However, there is a possibility that the convex-concave shape of the recording layer may impede the stable flying characteristic of a magnetic head and thus cause a problem of head crash or the like. From this point of view, JP-A-H10-222944 discloses a recording medium in which the convex-concave shape changes in a track width direction for the purpose of achieving the flying stability of a magnetic head.
Further, JP-A-2000-195042 proposes a discrete type magnetic recording medium in which concave portions in the convex-concave shape are filled with a nonmagnetic material or another material for ensuring the stability in flying characteristic of a magnetic head.
On the other hand, JP-A-H06-111502 discloses a technique that defines a relationship among the width of each of rectangular tracking servo burst patterns formed by a convex-concave structure on a longitudinal recording medium, the track pitch, and the read width of a reproducing head.
In general, on a magnetic recording medium used in a magnetic disk drive, servo areas necessary for a magnetic head to perform tracking are recorded by a servo track writer.
The servo area generally includes an ISG (Initial Signal Gain) portion, an SVAM (SerVo Address Mark) portion, a Gray code portion, a burst portion, and a pad portion which are in the form of various magnetic patterns for exhibiting predetermined functions, respectively.
The magnetic patterns of the burst portion are each normally recorded with a width equal to about one track pitch in a radial direction of the magnetic recording medium. On the other hand, the ISG portion, the SVAM portion, the Gray portion, and the pad portion are each normally recorded continuously in the disk radial direction over several tracks or entirely.
The burst portion is in the form of the patterns for providing precise position information necessary for the magnetic head to perform accurate tracking to the track position. Those patterns of the burst portion are normally (1) composed of a combination of first and second bursts each equally straddling a center line that defines the track pitch between adjacent tracks or (2) composed by adding thereto a combination of third and fourth bursts each located at a position offset from the first and second bursts by half the track pitch.
One example of the tracking operation in the simplest combination of the first and second bursts will be given as follows. Specifically, when a magnetic head has passed through the first burst and the second burst in order, a reproduction signal Sa from the pattern of the first burst and a reproduction signal Sb from the pattern of the second burst are compared therebetween by the use of a differential amplifier to derive a value of a position error signal PES=(Sa−Sb). The value of the position error signal PES=(Sa−Sb) is input into a servo control circuit to thereby drive a tracking servo actuator according to the magnitude of the position error signal to operate the magnetic head such that the center of the magnetic head follows the center of a data track.
However, the burst patterns of the conventional discrete medium are each a rectangular pattern. Although the rectangular patterns are ideal for obtaining an accurate position error signal, a very high accuracy is required in terms of shape and dimensions when forming the rectangular shape.
Accordingly, it can be said that a production load in processing is extremely large in terms of the required very high formation accuracy.
The present invention has been made under these circumstances and has an object to provide a magnetic recording medium having a burst pattern shape that can largely reduce a production load in processing and still can obtain an accurate position error signal and further to provide a magnetic recording and reproducing apparatus using such a magnetic recording medium.